Although the clinical features of ulcerative colitis (UC) and Crohn~s disease (CD) have been well described, the etiopathogenesis of these chronic relapsing IBDs remain unknown. There is convincing evidence, however, that IBD is characterized by the inability to downregulate acute inflammatory responses which is the result of an imbalance between pro-inflammatory and anti-inflammatory factors within the gut mucosa. Our laboratory has demonstrated that the balance between interleukin-1 (IL-1) and its natural antagonist, the IL-1 receptor antagonist (IL-1ra), may be a primary factor involved in the pathogenesis of chronic intestinal inflammation (see Progress Report). Using genetic and molecular biology techniques, the present proposal is designed to investigate the factors which regulate the synthesis of IL-1 and IL-1ra during intestinal inflammation in IBD. The overall objective is to understand the molecular mechanism(s) involved in the pathogenesis of chronic inflammation in IBD and which factors predispose affected individuals to the disease. The specific aims of this proposal are: (1) To determine the role of IL-1 and IL-1ra genetic polymorphism in IBD. Utilizing an association approach with specific markers is case control panels with different ethnic backgrounds and performing linkage analysis in multiplex families, both with and without the associated alleles, we will define the role of IL-1 and IL-1ra in IBD susceptibility. (2)To examine the functional significance of IL-1 and IL-1ra genetic polymorphisms. Using specific immunoassays, we will measure IL- 1alpha, IL-1beta and IL-1ra production rates in plasma, cells and tissues from IBD patients, and correlate their relationship to other genetic and subclinical markers associated with IBD. (3) To investigate the transcriptional regulation of intestinal mucosal IL-1ra. Using electrophoretic mobility gel shift assays with DNA probes derived from IL-1ra promotor fragments (recently identified as critical for the expression of the two human IL-1ra isoforms) we will determine the presence or absence of specific protein/DNA complexes which may be involved in the dysregulated synthesis of IL-1ra in IBD. (4) To evaluate the role of novel genetic polymorphisms of immunoregulatory cytokines which affect IL-1ra synthesis. We will characterize novel polymorphisms of cytokine genes, such as IL-10, which are important in the regulation of IL-1 and IL-1ra production, and determine their association with UC and CD. The ultimate goal of the present research proposal is to further characterize the pathogenesis of IBD by identifying those factors which contribute to the predisposition and perpetuation of chronic intestinal inflammation.